1. Field of the Invention
The present invention relates to a method of data modulation and an apparatus for and a method of recording data on and/or reproducing data from a recording medium, and more particularly, to a data recording and reproducing apparatus and method in which data are modulated to be resistant to channel distortion.
2. Description of the Related Art
With the increased recording density of recording media, track pitches of digital versatile disc random access memories (DVD-RAMs), recordable DVD (DVD-R), or DVD rewritable (DVD-RW) become narrow. Accordingly, introduction of crosstalk or noise from neighbor tracks and the amount of inter-symbol interference (ISI) from neighbor pits are increasing. This disturbance increases jitter of a radio frequency (RF) signal, particularly when a recording medium whose physical address is recorded as pits is accessed.
Run length limited (RLL) codes having limited maximum and minimum run lengths are common data modulation codes for recording media. The minimum run length, which is denoted by parameter “d”, greatly affects accuracy in detecting pits (or lands) in an optical disc and the recording density of that code. The maximum run length, which is denoted by parameter “k”, is associated with code efficiency and sync strategy. Common RLL codes include consecutive run lengths between the minimum and maximum run lengths “d” and “k”. For example, eight-to-fourteen modulation plus (EFM+) codes compatible with DVD family recording media have d=2 and k=10, so 4T, 5T, . . . , 10T (where T=reproduction clock) codes, excluding a sync code, exist between a minimum pit (or land) length of 3T and a maximum pit length of 11T. FIG. 1 is a histogram of the run length distribution of the EFM+ codes. However, when jitter occurs in an RF signal being reproduced, due to any distortion in a channel, the 1T space codes of FIG. 1 increase the likelihood of error occurring at a deviation of ±0.5T.
FIG. 2 is a table of the physical address format in the header field of a general DVD-RAM. For the general DVD-RAM, the same address data are written twice to the header field for high detection performance. The physical address format includes variable frequency oscillator (VFO1) data for phase locked loop (PLL), address mark (AM) data, physical identification data (PID1), identification error detection data (IED1), and postamble data (PA1) for IED1 demodulation. VFO2, AM, PID2, IED2, and PA2, which have the same functions as VFO1, AM, PID1, IED1 and PA1, respectively, are also included in the address format. However, even though detection performance is improved, writing the physical address data based on this RLL modulation code causes a redundancy problem.